1. Field of the Invention
The present invention generally relates to a display driver, and more particular, to a light emitting diode (LED) driver and a display device using the same.
2. Description of Related Art
Recently, many electronic products are equipped with displays, such as mobile phones, personal digital assistants (PDAs), digital music players, and automobile instrument panels. Types and sizes of the displays are usually designed according to their practical applications. However, almost all displays including liquid crystal displays (LCDs) need backlight modules to provide backlight illumination thereto, and thus designers must design illumination circuits for the displays for allowing users to clearly view patterns and letters displayed thereon. LEDs are often adopted in current electronic products as illumination devices. Generally, three or four or even more LEDs are needed for a uniform backlight provision for a colourful LCD, and six or more LEDs are required for an instrument panel backlight provision. As demand for LEDs increases, market for LED drivers is drastically driven to increase accordingly.
FIG. 1 is a circuit of a conventional device. Referring to FIG. 1, the conventional device uses a backlight module 100. The backlight module includes LED drivers 110, 120, and 130 respectively including red, green and blue LED sets 113, 123, and 133. As shown in FIG. 1, all circuits for respective LED drivers 110, 120 and 130 are conventional boost circuit. Each of the LED sets 113, 123, and 133 are composed of serially connected LEDs of same color. In other words, a controller 117 can be used to control a loop composed of only one switch 112 and one feedback circuit 115. Therefore, the boosting of the LED driver 110 can be realized by driving only a single loop to control a single LED set 113.
The aforementioned three LED drivers 110, 120, and 130 have same circuit structures. Each of the three LED drivers 110, 120, and 130 can independently adjust the input voltage VI, providing respective corresponding LED sets 113, 123, and 133 an independent adjustment current. For example, the LED driver 110 is composed of the controller 117, a main switch 116, an inductor 111, the switch 112, the feedback circuit 115, and a voltage stabilizing circuit 114.
Because one LED driver can drive only one LED set, three LED sets require three LED drivers when LED sets of three different colors are needed for driving. LED sets of different colors also require different voltage drop, according to which inductances of respectively the inductors 111, 121, and 131 are selected.
Therefore, conventional device requires one independent LED driver for driving each LED set. As such, although simple, such a conventional device has LED drivers, whose area proportionally increases as the LED sets increases.
In summary, a disadvantage the convention technology for LED drivers is that it can control a single loop, thus each LED set requires individually designed LED driver. Such a conventional technology requires relatively large area for circuit. Accordingly, issues to be considered when designing products having LED drivers are: larger circuit area causes greater product's bulkiness; usage of more LED drivers increase production cost. Accordingly, conventional technology unfortunately requires too much circuit elements that occupies too much circuit area. As such, the circuit board thereof becomes very complicated. When also considering the greater bulkiness, such LED drivers are inconvenient for application.